In accordance with knowledge in the cardiac pacemaker art, the use of so-called DDD cardiac pacemaker systems is recommended in relation to appropriate pathological results. That specification “DDD” (Dual pacing/Dual sensing/Demand+Triggered) means that on the one hand stimulation (“pacing”) is effected in both heart chambers and that, on the other hand, innate actions in respect of the sinus or AV node of the heart, which are still present, are detected both in the atrium and also in the ventricle (“sensing”). So-called “double lead” DDD pacemaker systems are already known for that purpose. The main disadvantages thereof however is that two separate electrode probes have to be implanted into the heart and positioned there.
Single probes are also known in which a ventricular electrode is arranged at the probe tip and two atrial ring electrodes are arranged at a corresponding distance from the ventricle electrode on the probe body. The atrial ring electrodes are used to detect the atrial potential, whereby ventricular stimulation is triggered after a suitable atrio-ventricular delay. Ventricular stimulation can be effected in bipolar manner. In principle it is admittedly possible for the above-discussed single electrode probe also to be used for DDD cardiac pacemaker systems. A problem which arises here however is that the atrial ring electrodes are not placed in an established position on the wall but float freely in the blood stream. These so-called “floating” electrodes in the atrium result in serious limitations in terms of the stimulation properties as generally very high stimulation amplitudes have to be used. The main reason for this is the lack of on-wall established placement of the floating electrodes. The high stimulation amplitudes entail the disadvantage of a high level of energy consumption and frequent phrenic stimulation effects.
In comparison, published European Patent application 0 779 079, by Boehm and Bolz, discloses a single electrode probe (referred to as a single lead) which, on the part of its length which in the implanted condition is placed in the atrium, is of such a shape that at least one atrial electrode—usually a ring electrode—of the probe can be caused to bear in an established position against the wall of the atrium of the heart. In order to achieve that the probe is provided over that part of its length with an elastic pre-shaping element which imparts to the probe there a definedly deflected shape. By virtue of its elasticity however the pre-shaping element can be transferred from its defined configuration into a substantially straight stretched condition, which is effected by means of the usual guide wire used in the probe implantation operation. It will be appreciated that in that respect the guide wire must be significantly stiffer in regard to its elasticity properties than the pre-shaping element.
In the implantation procedure prior to implantation of the probe the guide wire is advanced until it comes to a stop against the tip of the probe, in which case that advance movement of the guide wire causes the application to the probe body of a pulling force which results in stretching of the probe in the region of the pre-shaping element. The probe can then be introduced into the heart in that stretched condition. After implantation of the probe and withdrawal of the guide wire the probe is then so designed over the above-mentioned part of its length by virtue of its pre-shaping element that the probe bears with at least one atrial ring electrode against the wall of the atrium of the heart. The relatively complicated configuration of that single electrode probe is found to be a disadvantage in that respect. In addition using a guide wire in implantation of the single electrode probe is not desirable.
Published European Patent application EP 0 426 089, by Cohen and Thacker, discloses an electrode arrangement with two separate electrode probes, wherein one of the electrode probes is introduced into the atrium and further into the ventricle, while the other electrode probe is fitted as a counter-electrode externally to the heart, that is to say as an endocardial counter-electrode. Provided at the distal end of the electrode line is a helix electrode 25 as a tip electrode which is fixed in the right ventricular myocardium by virtue of being screwed therein. Above the tip electrode a section of the line is divided into two, wherein both portions of the divided section each have a respective coil electrode 22, 24 for defibrillation purposes. The two branches are biased relative to each other so that they are arranged in mutually spaced relationship in the implanted condition. In this case the electrodes 22, 24 are intended to form a contact with the right ventricular myocardium. The two-part electrode line and the electrodes 22, 24 were selected here in order, with the endocardial electrodes 18, 20, to form a quadrilateral polygon (orthogonal electrode placement). A disadvantage in this arrangement however is that two separate electrode probes have to be implanted. In addition the electrode line is adequately fixed only in the ventricle so that the electrodes in the atrium are in the form of floating electrodes. Electrical contact of the tip electrode in the ventricle can readily be ensured while the electrical contact in the atrium can be critical and thus suffers from the above-discussed disadvantages. In addition, the prerequisites for fixing electrodes in the atrium are different from those involved in fixing electrodes in the ventricle as the atrium essentially involves a “passageway”.
U.S. Pat. No. 4,154,247, to O'Neill, has a FIG. 4f that shows an electrode line with a branched section 620 that, as illustrated in the Figure, is intended for placement in the ventricle but which in accordance with the description can also be placed in the atrium of the heart. This patent, however, says nothing in regard to fixing the electrode line.
The object of the invention is to provide an electrode line to be fixed in the atrium of a heart.